Electronic golf swing analyzers have been used to assist people with monitoring characteristics of their individual golf swing. Some configurations generally use some form of light detector (e.g., phototransistor, photo cell, etc.) as a sensor for use in swing analysis. However, the prior art designs suffer from the same limitation wherein they perform adequately indoors with a stationary overhead light source, but fail to operate properly when utilized outdoors. More specifically, measurements of conventional swing analyzers become erratic and inaccurate in the presence of the moving sun during outdoor use. These machines are not reliable when used outdoors.
Referring to FIG. 1, one conventional optoelectronic golf swing analyzer configuration is shown. An array of light sensors 12 is imbedded in a hitting platform 10 in reasonably close proximity to a golf ball 11 to be struck by an approaching golf club 14. A lamp 13 is mounted in a fixed position above sensor array 12 to provide a source of infrared light for sensor array 12.
As the clubhead of golf club 14 approaches golf ball 11, the light is blocked from some of the sensors of array 12 and this condition is subsequently detected. Sensor array 12 is arranged in a specific pattern that allows detection of the position and timing of the clubhead of club 14 in the impact area of golf ball 11. From this data, important information about the golf swing can be calculated and displayed. For example, clubhead path, clubface angle, clubbead speed, impact point of ball upon the clubface, tempo or swing time, ball velocity and ball carry are exemplary parameters which may be calculated and displayed to the user.
The type of device illustrated in FIG. 1 functions properly when used indoors with a fixed overhead light source, such as lamp 13. However, when the device is used outdoors and especially in the sun, several factors have a negative influence on performance which preclude accurate detection of clubhead timing and position.
FIG. 2 shows a typical sensor circuit for a conventional optoelectronic swing analyzer arrangement. The depicted circuit comprises a light detector 21 coupled with a resistor 22 and comparator circuit 23. A steady state source of light 20 from lamp 13 (not shown) illuminates light detector 21 which provides a high signal output (+V) due to the light current flowing through resistor 22. When the clubhead passes over light detector 21, the light current is reduced and the output signal goes to a logic low (0) state. The output signal is routed to logic gate or comparator 23 which detects this change in output signal from resistor 22. The change in the output signal indicates the passage of the clubhead.
Referring to FIG. 3-FIG. 5, problems typically experienced with the utilization of such conventional devices in the outdoors is illustrated. If the analyzer is exposed to the sun, device operation becomes erratic inasmuch as sunlight contains more intense infrared energy than the overhead lamp. Thus, sensors 21 tend to respond to the presence or absence of sunlight.
Further, other sources of error can be attributed to the fact that the sun is constantly moving such that the light source for the detectors comes from many different directions depending upon the time of day. A plurality of sensors 21 are sequentially labeled 1 thru 13 in FIG. 3-FIG. 5. The sun is directly overhead in the illustration of FIG. 3 and plural light rays 30 therefrom radiate straight down casting a shadow 31 directly under the clubhead of club 14. Sensors 21 numbered 4 thru 8 are blocked from light 30 in FIG. 3.
The position of the sun in FIG. 4 is to the right of club 14 and light rays 30 are angled from right to left in a downward direction creating shadow 31 that lags the clubhead of club 14 (assuming the clubhead is moving from left to right in FIG. 4). Sensors 21 numbered 1 thru 6 are blocked from the sun in FIG. 4 although the position of the clubhead of club 14 with respect to sensors 21 is identical in FIG. 3-FIG. 5.
The sun is to the left of club 14 in FIG. 5 with light rays 30 angled from left to right in a downward direction creating shadow 31 that leads clubhead 14 (again assuming movement of the club in a direction from left to right). Sensors 21 numbered 6 thru 12 are blocked from light 30 from the sun in this case.
Although clubhead 14 is in the same exact position in the above illustrations with respect to sensors 21, the actual sensors 21 that are blocked from the light source (e.g., the sun) change as the light source moves. This creates errors in measurement of clubhead position. Furthermore, any given sensor 21 is blocked from the light source at a different time during the swing as the sun moves across the sky. This creates errors in timing measurements.
The problem is further complicated by the fact that the intensity of the light seen by the sensors 21 also changes as the sun moves. The light is most intense when the sun is directly above sensors 21 as shown in FIG. 3, and least intense in the morning and evening hours corresponding to FIG. 4 and FIG. 5. Other sources of measurement errors include reflections of light from the leading edge of the clubhead and shadows cast by nearby objects across the array of sensors 21.
One way to reduce problems associated with the use of conventional devices outdoors includes completely shading all sensors 21 of this type analyzer from sunlight so that only light from overhead light 13 reaches the light detectors 21. Such could include using the analyzer in a tent with the associated costs and inconvenience.
As is readily apparent, the above configurations prove problematic in a prime desired application of the analyzer--use outdoors. Further, the suggested solutions have associated drawbacks which reduce the attractiveness or feasibility of utilizing the conventional devices outdoors.
Referring to FIG. 6 and FIG. 7, another technique used in some conventional configurations to detect a clubhead is illustrated. An emitter 34 is positioned to radiate a steady beam of light 35 in an upward direction. When the clubhead of club 14 passes over light 35, a portion of the light is reflected down and increases the light current through a phototransistor 37 which produces a voltage response across an associated resistor 38.
These circuit configurations will typically not operate properly in direct sunlight because infrared energy emitted from the sun is much more intense than that of emitter 34. Accordingly, any change in phototransistor current caused by sunlight will overpower any small change in current due to reflected light energy 35.
Some devices have been designed to use horizontal beams of light energy in an effort to overcome problems caused by sunlight. The emitters and detectors are housed in boxes that protect associated sensors from direct sunlight. Such sensors are typically configured to detect the moment a clubhead breaks a horizontal beam of light. There are a number of patents that describe such devices, including U.S. Pat. No. 5,692,966, U.S. Pat. No. 5,257,084, U.S. Pat. No. 5,324,039 and U.S. Pat. No. 5,087,047.
A significant drawback with these designs is that the devices are usually restricted to calculating timing measurements of the moving clubhead without providing position measurements. Therefore, such devices are limited to measuring clubhead speed and tempo. Additional important swing parameters such as clubhead path, clubface angle and the impact point of the ball on the clubface require position information of the clubhead.
Therefore, a need exists to provide a sensing system and methodologies that overcome the limitations of the above-described configurations, and produce accurate measurements both indoors and outdoors, and during night or day.